Marketable Securities - Carrying Amounts of Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Marketable Securities [Line Items]
Short-term marketable securities	$ 49,968	$ 56,088
Long-term marketable securities	67,234	55,342
Held-to-Maturity [Member]
Schedule of Marketable Securities [Line Items]
Short-term marketable securities	49,968	56,088
Long-term marketable securities	67,234	55,342
U.S. Government and agency obligations [Member] | Held-to-Maturity [Member]
Schedule of Marketable Securities [Line Items]
Short-term marketable securities	10,000	7,375
Long-term marketable securities	67,234	55,342
Commercial paper [Member] | Held-to-Maturity [Member]
Schedule of Marketable Securities [Line Items]
Short-term marketable securities	39,968	34,966
Municipal bonds [Member] | Held-to-Maturity [Member]
Schedule of Marketable Securities [Line Items]
Short-term marketable securities	0	8,738
Corporate bonds [Member] | Held-to-Maturity [Member]
Schedule of Marketable Securities [Line Items]
Short-term marketable securities	$ 0	$ 5,009